Distribution of carbonic anhydrase in cells and membranes isolated from pig gastric mucosa.

Mucosal cells were isolated from pig stomachs and then fractionated on linear density gradients of Percoll. Different types of cells were identified by their typical staining and morphology. In disrupted cell fractions, hydration of CO2 by carbonic anhydrase was measured by means of pH-stat technique. Localization of carbonic anhydrase to certain cell fractions was also studied by histochemical staining. Both parietal cells and carbonic anhydrase were confined to the low and intermediate density fractions of the gradients. Purified membranes from pig gastric mucosa, which contained the acid pump of the stomach, the H,K-ATPase, also contained a firmly bound carbonic anhydrase of high activity. The enzyme activity in the membranes was inhibited by acetazolamide, furosemide and KSCN. The molecular mass of the carbonic anhydrase was 33 kDA as estimated by its binding of [14C]furosemide followed by polyacrylamide gel electrophoresis. Previous suggestions of a role of carbonic anhydrase as a supplier of H+ in the secretion of acid are supported by its high activity and its localization to the same membrane as the acid pump of the stomach.